Engines, including diesel engines, gasoline engines, gaseous fuel-driven engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous and solid material, including particulate matter, nitrogen oxides (“NOx”), and sulfur compounds.
Due to heightened environmental concerns, exhaust emission standards have become increasingly stringent over the years. The amount of pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of particulate matter and NOx exhausted to the environment has been to remove these pollutants from the exhaust flow of an engine with an aftertreatment system that includes filters. However, using filters for extended periods of time may cause the pollutants to buildup in the components of the filters, thereby causing filter functionality and engine performance to decrease.
The collected particulate matter may be removed from the filter material through a process called regeneration. A particulate trap may be regenerated by increasing the temperature of the filter material and the trapped particulate matter above the combustion temperature of the particulate matter, thereby burning away the collected particulate matter. This increase in temperature may be effectuated by various means. For example, some systems may employ a heating element to directly heat one or more portions of the particulate trap (e.g., the filter material or the external housing). Other systems have been configured to heat exhaust gases upstream of the particulate trap. The heated gases then flow through the particulate trap and transfer heat to the filter material and captured particulate matter. Such systems may alter one or more engine operating parameters, such as the ratio of air to fuel in the combustion chambers, to produce exhaust gases with an elevated temperature. Alternatively, such systems may heat the exhaust gases upstream of the particulate trap with, for example, a burner disposed within an exhaust conduit leading to the particulate trap.
One method of regenerating a diesel engine exhaust filter is described in U.K. Patent Application Publication No. GB 2 134 408 A (“the '408 publication”) to Wade et al. The method for regenerating the exhaust filter described in the '408 publication includes bypassing all of the exhaust gas around the filter through a duct, supplying combustible gas to the filter at a low flow rate, and raising the temperature of the combustible gas to ignite the filter. When the temperature of the heated combustible gas leaving the filter exceeds a predetermined limit, the regeneration process is completed and the exhaust gas is allowed to flow through the filter again.
Although the system of the '408 publication includes a particulate trap for capturing particulate matter, all of the exhaust gas is directed to bypass the filter when the filter is being regenerated. Therefore, none of the particulate matter is removed from the exhaust gas during the regeneration process.
Also, although the particulate trap of the '408 publication may be able to remove particulate matter from the exhaust gas, the trap does not remove other types of pollutants in the exhaust gas, such as NOx emissions and sulfur compounds.
Furthermore, the heated gases that flow toward the particulate trap may damage any temperature-sensitive components downstream from the particulate trap. Components that may be damaged or less efficient at high temperatures include some catalysts for removing pollutants from the exhaust gas by chemical reaction. Components that are made to withstand higher temperatures, such as the temperatures required for regeneration, are typically more expensive.
The disclosed system and method are directed to overcoming one or more of the problems set forth above.